1. Field of Invention:
This invention relates generally to an anchor and stress plate assembly for securing an insulation layer to the deck of a roof, and more particularly to an assembly of this type whose anchor turns into decking material but does not penetrate the underface thereof.
2. Status of Prior Art:
It is common practice to cover the roof of a building with a layer of thermal insulation formed of pads or panels of lightweight material such as fiberglass or rigid foam plastic. These panels are laid down on the roof deck and covered by a sheet of polyvinyl chloride, or other water-impermeable membrane to protect the layer against water penetration.
Since the roof is exposed to the elements, it may on occasion be subject to high velocity winds as high as 150 miles per hour. Unless the insulation layer is firmly secured in place, the resultant updraft may blow the layer off the roof. For various reasons such as fire protection, the use of bonding agents to adhere the insulation layer to the deck of the roof is being discontinued, and instead mechanical fasteners are now employed to retain the layer when a strong updraft is encountered. The present practice of securing the insulation layer to the roof deck is by means of load-bearing plates of sheet metal which overlie the insulation layer and are bolted or otherwise mechanically fastened to the deck.
Among the patents which disclose load-bearing or stress plates for this purpose are the Giannuzzi patent 4,574,551, the Williams patent 1,286,862, the Sandquist patent 4,074,501 and the Carlson patent 4,288,951.
The concern of the present invention is with an anchor and stress plate assembly usable with two types of decking material. One is relatively soft, such as a porous wood and fiber composite known commercially as Tectum. The other is a hard decking material such as gypsum, plaster board, or low strength cement. By "a hard decking material" is meant one which when a hole is drilled therein is capable of being tapped by an auger screw. It is important to note that such hard deck materials are also somewhat brittle and therefore subject to disintegration by an anchor screw unless the screw is of the proper type.
Conventional anchor and stress plate assemblies for these two types of decking materials usually make use of anchors of the toggle type which penetrate the material. Hence when the assembly is installed, the stress plate then engages the upper face of the insulation layer while the toggle then engages the underside of the deck. A serious practical shortcoming of this conventional arrangement is that the toggles are exposed at the underside of the deck and deprive the underside of a clean, finished appearance. When the deck underside forms the ceiling of the building interior, the presence of toggles on this ceiling is unsightly and therefore not commercially acceptable.
Another drawback is that anchors in the form of conventional toggle bolts tend to loosen up as a result of vibratory or other forces, and sometimes in doing so cause debris to fall into the interior of the building. And in loosening up, the anchor may in time fail and result in a blow off of the insulation layer held thereby.
In order to provide an assembly including a nonpenetrating anchor for soft decking materials such as Tectum, the Blucher et al. patent No. 4,642,012 provides an auger-like anchor whose shank is composed of three sections of different diameter, the head of the screw being received in a washer functioning as a stress plate. No means are provided in this assembly to resist loosening of the anchor.